Hydrocyclones are used in mining processes to separate two streams of material into overflow and underflow streams. Many process variables must be controlled to create a dynamic condition for excellent separation. It is not unusual for roping, plugging, or other undesirable conditions to occur due to materials or speeds or other conditions.
Classification is a critical component of any minerals milling circuit. Hydrocyclones efficiently separate mill discharge, returning coarse material to the mill and sending fine materials to downstream processing, such as flotation. Due to process abnormalities, hydrocyclones may plug or develop an underflow condition referred to as “roping.” Whenever a hydrocyclone is roping or plugged, large amounts of coarse, misplaced material may end up in hydrocyclone overflow and downstream float cells. Once roping occurs, the separation process becomes unsatisfactory. When plugging occurs, the process stops altogether, requiring excessive manpower to clean out and restart the process.
In prior systems, operators had no indication of roping before the problem occurred. To determine which of many hydrocyclones may be roping, an operator had to climb to the top of a group of hydrocyclone units (also referred to herein as a “pack” of hydrocyclones) to see which unit was not operating properly.
One attempt to address the roping detection problem involves attaching ultrasonic sensors to an underflow portion of the hydrocyclone. As the underflow approaches roping, the underflow hits progressively lower on the hydrocyclone splash skirt and eventually misses the splash skirt altogether. The corresponding changes in ultrasonic signal strength are processed to aid in recognition of roping and to generate an alarm when roping occurs. Unfortunately, ultrasonic energy in the 40 kHz frequency range is substantially attenuated by elastomeric liner materials, interfaces, gaps and boundaries, and distance, all of which are present in hydrocyclone applications. Furthermore, all of these attenuation conditions can change from time to time during normal operation.
What is needed, therefore, is a reliable method to detect the onset of roping, plugging, and other adverse conditions and to immediately notify the control room as to which hydrocyclone unit is experiencing a problem. In particular, a detection method is needed for monitoring both the overflow and the underflow conditions of a hydrocyclone using vibration analysis. The desired method performs vibration analysis in sonic frequency ranges, as opposed to the ultrasonic frequency ranges of previous applications.